Driven by a desire to find new structural polysaccharides using enzymatic syntheses or genetic engineering of microorganisms, researchers have discovered polysaccharides that are biodegradable and can be made economically from renewably sourced feedstocks. One such family of polysaccharides are alpha-glucans, which are polymers comprising glucose monomers linked by alpha-glycosidic bonds.
Dextrans represent a family of complex, branched alpha-glucans generally comprising chains of alpha-1,6-linked glucose monomers, with periodic side chains (branches) linked to the straight chains by alpha-1,3-linkage (loan et al., Macromolecules 33:5730-5739). Production of dextrans is typically done through fermentation of sucrose with bacteria (e.g., Leuconostoc or Streptococcus species), where sucrose serves as the source of glucose for dextran polymerization (Naessens et al., J. Chem. Technol. Biotechnol. 80:845-860; Sarwat et al., Int. J. Biol. Sci. 4:379-386; Onilude et al., Int. Food Res. J. 20:1645-1651). Although dextrans are used in several applications given their high solubility in water (e.g., adjuvants, stabilizers), this high solubility can negatively affect their general utility as thickening agents in hydrocolloid applications.
Thus, there is interest in developing new, higher viscosity dextran polymers that are more amenable to high viscosity applications. In turn, there is also interest in identifying glucosyltransferase enzymes that can synthesize such dextran polymers.